Early
texts describe "The Catlin Grip" as "like holding a pen" and
illustrate the hand in - ta-da - the position of function. See
the photo attached. But sometime in the beginning of the 20th
century, the pictures were redrawn, showing the wrist flat.
And that became the defacto default. The picture shows the
Catlin Grip which is what was used by Chris NW6V to win 1st
place in straight key sending contests.
Many radiotelegraphers - myself included - send with a straight key and never get glass arm because I evolved away from a flat wrist posture. I never use my wrist to send with. I use my arm my wrist is totally limp. Instructors in Morse when I learned would come around to see if your wrist was tense, if it was your posture was incorrect as you were using your wrist, and not your arm which is the correct posture.
With sending with both a semiautomatic key (bug) and a sideswiper, I use the lower arm, NOT the wrist to send. The wrist is totally limp.
73
DR